Sharif Digital Repository

The AASHTO Standard Specification defines diaphragms as a transverse member between girders in order to maintain sectional geometry. Some of the reasons in favor of using a diaphragm are that it prevents the girders from twisting during the process of construction and helps in distributing vertical live loads between girders and transfers lateral loads (wind or earthquake) to supports. It also provides restraint for the lateral-torsional buckling of the girders. While diaphragms at the ends of bridges are called end diaphragms, the diaphragms away from the bridge ends are called intermediate diaphragms. These members are usually made of steel or cast-in-place concrete. Based on their... 

Following inadequate performance of bridges during the past earthquakes, serious attention has been drawn to evaluation of seismic vulnerability of existing bridges and retrofit measures. This research surveys seismic performance of existing bridges according to the latest manual for seismic rehabilitation of highway bridges in America (FHWA2006). This manual introduces six different methods which vary considerably in sophistication, rigor and applicability. This research is based on method D2 (Nonlinear Static Procedure or Pushover Method) in which the seismic demands are determined by elastic methods such as multi-mode response spectrum, or elastic time history method and capacity... 

Post-tensioning is the most versatile form of prestressing, a technique which enables engineers to make the most effective use of the material properties of concrete, and so to design structural elements which are strong, slender, and efficient. Design of post-tensioned concrete structures is not difficult and, if done properly can contribute significantly to the economy and the aesthetic qualities of a structure. Post-tensioned building floors and bridge girders have found widespread use in office buildings, parking structures and bridges. They are also frequently employed in warehouses and public buildings. Now a days bridges and other type of structures, in many countries are designed... 

In this research the appilication of a new method named Endurance Time (ET) analysis in seismic analysis of multi span bridges in linear and nonlinear ranges is investigated. Endurance Time is a time history based method of seismic analysis. In this method structure is subjected to an intensifying predefined acceleration function and different damage indices of the structure are evaluated through analysis time. The Endurance Time criterion and the Endurance Time acceleration functions have been generated in previous researchs of ET group. Using 7 earthquake records which are selected from hundred ones of PEER database based on FEMA p695 recommendations, several scaling methods are used to... 

In recent years, the application of base isolation as a seismic design strategy for reducing the effects of earthquake ground motion has become an advantageous method and much effort has been devoted to base isolation research and there has been a growing acceptance of this approach. In this research, the effect of using base isolators in reducing the dynamic forces of piers and abutments of bridges is studied. More specifically double-span bridges are the target of this research. After modeling a regular bridge in a typical analysis program, it is excited by different earthquake accelerograms and then the effect of using base isolators in dissipating the earthquake energy is investigated  

A large number of bridges in Iran are deteriorating under long and heavy traffic loadings, while getting closer to the end of their design life time. Therefore, many of them have been exhibiting various problems such as excessive vibration or large deflection under the normal service loadings. So, mitigating traffic-induced bridge vibration and damages is necessary to extend their efficient period of serviceability. On the other hand, application of active and passive control devices in structural retrofitting have absorbed the attention of many engineers and researchers. In this work, the performance of an active control system made of piezoelectric actuators is investigated in reducing the... 

Due to large range searches (there are various alignments between two points) as well as the complex and non-linear cost functions and a variety of geometric constraints, the problem of optimal railway alignment is known as a difficult problem. For this reason, choosing an alignment between two points is usually done based on a limited number of alignments put forward by experts. In recent years, the study of the railway alignment optimization raised again due to the importance of optimization and introduction of various algorithms and their progress in solving various problems. It is expected that applying metaheuristic optimization algorithms, such as methods based on Swarm intelligence... 

Bridges are among the crucial elements of transportation networks and play an important role in facilitating emergency relief efforts following earthquakes. For this reasons, they should have an appropriate performance in earthquakes; Thus, presentation of true design of bridges was necessary. Elastic design of bridges due to the earthquake is uneconomic; hence, during an earthquake, the codes permitted to structures go to their inelastic behavior domain but inelastic analysis of structures are noncommercial and the capability of detail modeling of the inelastic behavior of the material is still impossible. Therefore, designers use response modification factor to consider the inelastic... 

This thesis targets the multidisciplinary area of time-variant seismic risk analysis of transportation networks. For this purpose, a new methodology and a library of probabilistic models are developed. Risk, in this context, denotes the probability of exceeding the sum of direct and indirect losses due to seismic events. Direct economic losses are due to the repair cost of the physical damage in the components of the network, such as bridges. The indirect losses are due to the reduced capacity of the components for traffic flow, which results in increased travel times in the network. This leads to socioeconomic losses. In this research, a reliability-based approach is adopted to carry out... 

Bridges are one of the most important parts of the transportation network and play an important role in relief after earthquakes. Therefore, detecting where and how much damage take place is vital. Bridge structure is consist of two parts: substructure and superstructure. Usually, superstructure remains intact during earthquake because of rigidity and high strength of it. In the other hand, damage localizes to substructure. We also use high safety factor to piles and cap piles so they experience little or no damage. As a result, columns suffer damage more than other parts. In this study, the focus is on columns damage. This study also is limited to non-prestressed multi-cell box girder... 

In recent years, due to the economical concerns in the structural design, many researches are devoted to introduce new frameworks for optimization of the construction cost as well as maintenance and rehabilitation costs in the life time. The bridges are the most crucial components of the transportation networks and their appropriate performances assures the flow in the transportation network. Hence, the reliability and response of such infrastructures especially in the emergency conditions and the state of servicibality after the hazards like earthquake play a key role in the social life. So far the design procedure of such infrastructures are only limited to the serviceability conditions as... 

Eliminating the tensile stresses and providing a cost-effective isolation system, has made the unbounded isolators an attractive option. Following this idea and the results obtained by various researchers, it is shown that unbounded steel-reinforced elastomeric bearings (SREBs), which are used and designed for service limit state, have inherently acceptable characteristics for a cost-effective isolation system and can provide improved structural performance. However, this inherent capacity is neglected in the design process.The current research presents an experimental program to analyze the mechanical properties of steel-reinforced natural rubber bearings without the upper and lower...